Twin fluke anchor



May 12 1942- R. s. DANFoRTH 2,282,566 l TWIN FLUKE ANCHR original FiledMarch 12. w41- ATTORNEY Patented May 12, 1942 UNITED STATES PATENTOFFICE TWIN FLUKE ANCHOR Richard S. Danforth, Berkeley, Calif.- Originalapplication March 12, 1941, Serial No.

382,943. 1941, Serial No.

Divided an d this application July 7, 401,323

1o claims.- '(01.114-208) .1941, and entitled Twin fluke anchors, now

Patent Number 2,249,546, of July 15, 1941. This case, as will presentlyhereinafter be set forth in detail, is concerned with an anchor whereinthe fluke area, fore and aft of the pivot mounting the ukes on theshank, is approximately balanced.`

For general purposes of classification and to delineate clearly thepresent invention, anchors can be divided into two groups, the so-calledkedge anchor and the stockless anchor. Briefly, the former includes ashank from one end of which projects two oppositely extending curvedarms carrying ukes or palms. At the other end, a long bar, the so-calledstock, is positioned in a plane transverse to that of the iiuke arms sothat one arm and its palm engage the ground'. Such an anchor istypically shown in the British Patent No. 6,004, of 1830, anchor (alsocalled the Admiralty anchor because of itspuse in the British Navyduring the nineteenth century) was later modified by Porter so the nukescould pivot on the shank as in United States Patent 2,497, of March 18,1842.

The latter type of anchor. the stockless anchor, is that commonly usedtoday on most merchant ships and by many navies because'of the ease withwhich it can be drawn up into a. hawse pipe and held there ready foruse. As commonly employed, it omits a stock; it includes a shank andtwin uke arms, usually secured together as a unit, pivoted at one end ofthe shank whereby both flukes engage the ground together. This anchorhas been variouslyconstructed but reference is made for a typicalshowing Ato the United States Patent No. 1,366,218, to Steele.

Many anchors of both typesphave been made and employed heretofore. Ingeneral, their hold? ing power, measured in pounds per pound of weighthas been low, of the order of from two to ten pounds per pound ofweight.

The holding power of an anchor is usually re-v ported together with areference to the type'of only a poor. or at the best only a fairanchorage with reference to anchor drag resistance.

' I have determined that the .twin-fluke type of anchor, as compared tothe kedge type anchor, is particularly susceptible to modificationswhich adapt it to continued penetration under continued pull toattainnally deep burial in the compact bottom offering the bestanchorage. This is due in part to the ground plowed up by the flukespassing by the sides of the shank instead of against its lower surfaceand so its burial resistance is lessened; because the undisturbed groundencountered by the shank during burial may pass back between the twoukes, and because there is no nonfunctional iiuke to resist burial. Inthose instancesI when the hard underlying bottom is at such a depth thatthe anchor cannot reach it, nevertheless the anchor of this inventionwill penetrate so deeply that it 4will to Perlng. The Perin'g bottom onwhich the test was made; for exam- V ple, a blue mud, a mud andshalebottom, etc.

The anchor would only engage this surface layer. and its resistancewould largely be merely that attendant upon pulling it through suchmaterial. Now .as a matter of fact, it has been observed that hard,relatively compact bottom will be foundunderneath almost any overlyinglayer offering given only insulcient reach a harder, more compact andmore resistive material at a` substantial depth to ensure a materiallyhigher holding power than any prior art anchor of similar weight underthe same circumstances. In these respects the twin-fluke'an-l chor. isfar superior to anchors of other types. and particularly to the kedgetype of anchor in which the flukes are so arranged that only one of themcan enter the ground at a time. Deep burial cannot be attained withanyother type of anchor. For these and other presently explained reasonsthe present invention is restricted to improvements in twin flukeanchors wherein the flukes engage the ground more or less simultaneouslyand cooperate in providingholding power.

`In developing an anchor which would bury itself consistently and bereliable in performance in other particulars, I found that merelyaltering one or two characteristics in various known anchors wasinsuiilcient for the anchor so achieved would, in some holding grounds,skid, furrow, rotate, or otherwise exhibit some failing making itunreliable in use. Some of the objectionable failings are as follows:

Floatlng" can occur mos't often on soft and muddy holding ground; thenukes lie at on theground surface or even inclined upward and do notfall into operating position even though the anchor is drawn over thebottom. An anchor of the twin iluke type may float on hard ground iflift at the fluke end. If grips are provided, as in some anchors, toensure the anchor does not float, then the anchor generally will notbury because its resistance is too high. Skidding" occurs when theanchor falls on its side and opens but rideson the forward end of thesha the point or side of one nuke and; the end o the stock, withoutdigging in. "Furrowing occurs in soft mud when the anchor rides alongwith one nuke superimposed, or nearly so, over the other end with oneend of the stock and one nuke only engaged with the ground. Rotation canoccur in ground of any type; at some point during the seating of theanchor but'before it has come to rest the downwardly acting forcesapplied to the two nukes become unbalanced, whereupon the anchor rotatesabout the shank axis and frees itself from ground engagement.

The anchor of my invention is sharply distinguished from prior artanchors,-and particularly those-of the twin fluke type, heretofore knownand employed, by the possession of certain characteristics.

Some of the critical factors which I have found are set orth here by wayof example. The order of the' appearance hereinafter does notnecessarily fiect the order of their importance, for,

asa m tter of fact, an anchor, to'operate satisfactorily, must' possessseveral fof the characteristics as will be presently explained,

First, the anchor is of the twin nuke type in which the shank passesbetween the nukes and both fiukes e age the ground more or lesssimultaneously nd cooperate to provide holding power; to ensure properfluke engagement and prevent rotation the-anchor is provided with atockor equivalent means.

econd, I have found that the nuke area must be proportioned relative tothe resistance area, both areas being hereinafter further defined withparticularity. When attention is given to this relation, in conjunctionwith the other characteristics, sufncient driving force is provided tocause the anchor to continue its downward penetration through softholding ground for a relatively indefinite distance or until harderground is reached. Generally stated, the nuke area should be as large asis practical andthe resistance areaas small as is feasible. I have foundthat certain minimum ratios should be observed between these areas toensure reliable performance.

Third, the nukes in operating position adopt certain dennite angularpositions. These are presently defined hereinafter in some detail. Takenas a measure of certain anchor operating characteristics, these angularrelations have been determined by me to fall within certain values tothe end that the fluke surfaces are most effective in their antagonisticfunctions of (l) producing initial burial with certainty, (2) thereafterurging the anchor downwardly until it is embedded in firm ground and (3)finally, holding the anchor stationary against the cable pull after ithas been firmly embedded.

Fourth, rotation of the anchor is prevented by giving attention to twofactors. First, the nuke areas are positioned with respect to each otherand with res ct to the axis of the shank, as hereinafter fur herexplained in detail, to minimize any tendency of the anchor to rotateunder pull. Second, the length of the stock relative to the nuke centerspacing is held above certain presently defined limits to overcome anyresidual rotational tendency. These two factors ensure absence fromrotation.

In addition to the foregoing I have found that the reliability ofinitial engagement is affected by the relation of the stock length toshank length and that to ensure reliable initial engagement thisrelation must be held within certain limits. Also, the crown of theanchor is so constructed as to ensure engagement without offercreasedholding powerper unit of weight- -the factor which, when coupled withstability and with dependability of engagement, provides the ultimatemeasure of value of anchors.

' Holding power is, by definition, resistance to further movement in thedirection in which the anchor is being dragged, and is dependent both onthe areas of the parts being moved through the ground, as projected to aplane normal to the direction of movementand to the intrinsic resistanceof the ground per unit of area. Thus theholding power of any anchor atthe surface of a soft mud bottom will be very small, by reason of thelow unit resistance of such ground, and to increase the holding powerthe anchor must continue to penetrate downwardly until firmer ground isencountered.

An anchor as herein described under continued pull continues thisdownward movement until the entire anchor is buried in nrmer ground, nomatter how much soft material may overlie it. It is this ability of myanchor to move downward to an indefinite distance in search of nrmholding ground which makes its holding power substantially independentof the nature of the bottomV on which the anchor is cast, there beingalways at some depth good holding ground beneath even the softest mud.

The exact manner in which holding .power of the highest order is securedwithout sacrificing certainty and stability will now be described, withreference to the attached drawing showing the presently preferred formof theranchor'of this invention. The preferred form of anchor of myinvention herein disclosed is particularly suited to manufacture fromhigh tensile strength steel. This permits small sections to be employedwith -extremely low resistance to burial. l' In the drawmg Figure 1 is aside elevation of the anchor in operating position.

Figure 2 is a plan view of the anchor shown in operating position inFigure l, while Figure 3 is a front view thereof.

Throughout this description and in the claims, the end of the anchor towhich the cable is attached will be referred to as the forward end, theend at which the fluke unit is pivoted will be referred to as the afterend.

In the form of anchor shown in Figures 1 and 2, a shank 5| is provided.This is pivotally mounted as at 52 on the nuke structure generallyindicated at 53 and which comprises the two generally triangularlyshaped nukes 54 and 55. Fluke structure 53 can be made up in anysuitable manner to provide a one piece nuke structure, as by boltingsubstantially identical halves together, with the shank pivotedtherebetween in a suitable manner. At the rear end of the nukes andadjacent the rear edge thereof crown portion 56 is provided. .Thisincludes rearwardly sloping faces 51 which engage the ground, as

sistance to burial.` An extension 58 is provided on each flukeandintegraltherewith, the extension serving as a stock. The extensionVas well as the rear edge portion which it continues is preferablythough not necessarily of arcuate contour, so that a minimum resistancearea is provided; the nukes can extend to each side along their rearwardedges to provide the functional equivalent of a stock.

The flukes 54 and 55 are preferably triangular in outline with theforward edges thereof at approximately an angle of 24. The inner edge ofeach 'fluke is formed with a rib 59 which slopes outwardly away from theadjacent shank at an angle of about 6 to prevent furrowing.

I shall now consider the various angular and dimensional relations whichI have found to be essential to or desirable for the production of highholding power coupled with reliability, first defining the terms used.

A is the pointof the cable attachment; B is the axis of the pivot, inthis-case the stock. The line B-'B is the axis of the stock; the lineC-D is the axis of the shank. f

The line E-F lies in a plane coinciding with the rforward or advancingfaces of the flukes. The points G-G are the respective centers of areaof the entire forward faces of the flukes. The points H-H are the pointsor forward ends of the flukes.

The effective shank length is the distance A-B from the point A of cableattachment to theaxis of the pivot; it is indicated by the dimension Kand is referred to herein as the shank length. The measurement Mis thedistance between the pivot axis B-B and the fluke. points'H-H and isreferred to herein as the overall fluke length.

The measurement P between the centers of area G--Gv of the .flukes istermed the fluke center spacing. The measurement R is the overall lengthof the stock.

The angle S between the plane of the fluke forward faces and a planepassed through. the point of cable attachment A and the centers of areasG-G of the forward faces oi the flukes,ris termed the. attack angle.

TheY angleT between the plane of the fluke forward. faces and the axisof the shank is termed the nuke angle.

'I'he angle U betweenthe plane of the fluke forward faces and a planeVpassed through cablel attachment point, A and the points or forward endsH-H of the flukes is termed thev point angle.

The fluke directional angle is measured between the inner. edge. of theiiuke and the axis of the shank when both are in substantially the sameplane.

The angle Y is the crown angle taken between the crown face and thefluke axis.

The angle X isfthe-uke point angle, between the inner; and outer forwardedges of the fluke.

The resistance area is the total sectional area ofthe anchor projectedparallel to the fluke axis with the nukes open, the projection beingmade onto a plane normal to this axis. It can be visualized as theshadow `cast on vlevel ground by the sun' in zenith when the anchor inoperating position (the flukes open) is held with the flukes pointingdirectly toward.v the sumand is' represented by the entire area inFigure 3.

The ilukearea is-thevsum of the areas'of the totali forward faces of thetwo flukes.

The several factors primarily characterizingran anchor of my inventionwill now be discussed, not in the order of'their importance, but ratheras I believe them logically related.

. Relation of fluke area to resistance area In the development of theanchor of the present invention I lfound that the fluke area should berelatively large as compared to the resistance area and that; in fact,the flukel area, in this form of anchor, should be at least 40% of theresistance Aarea Vand preferably 60% and as much as Aand more of theresistance area.

In those forms of anchors shown in Figures 1 and2, due to the relativelylarge fluke area and the thin sections employed, the iiuke area is over1.5 times as much as the resistance area.

When the importance of this relation is considered, it should beapparent that the fluke area must be so proportioned relative to theresistance area as to provide the burial force necessary to overcome theresistance provided by the purely functional portions of the anchor aswell as those Relation of resistance area to shank length Deep burialand its attendant high holdingV power are favored, I have found, byproviding a maximum downward driving force acting against av minimum ofresistance. From this it follows that the resistance area should beminimized to the greatest extent consistent with the strength requiredto avoid bending. or breakage. This is quite feasible with structuresembodying this invention for high tensile strength steels can beemployed.

Takingshank length as an approximately xed quantity for an anchor of anygiven size, and thereforefa basis to whichv other dimensions may bereferred, the resistance area as hereinbefore defined permlssible'in ananchor of any given size can be expressed as a function of shank length.To avoid comparison of an area with a lineal iigureV this relation isexpressed by comparing the resistance area with the square of the shanklength, in similar dimensional units.

Using this manner .of comparison I find that generally satisfactoryperformance can be expected when the resistance areaiI is not greaterthan 25% of the square Vof the shank length, and that the optimumperformance is obtained by holding the resistance area to a value lessthan 13%, and even more preferably 10%, of the square of the shanklength. f

Angular relations Possibly the simplest approach is to consider whatoccurs when an anchor is cast over the side to fall upon and engage thebottom under continued cable pull. Under any consideration the anchormust first engage the ground and then dig into the ground. It should notscratch the ground and drag along with the points of the nukes actinglike rakek teeth. To provide for reliable initial engagement I have,found that the point angle U should be taken into consideration and myexperience indicates that a point angle larger than 75 should be avoidedfor beyond this, while occasional engagement may occur, dependability isnot present; preferably this should be below 70. Since the point angle,according to definition, includes a consideration of shank length andother characteristics, in some instances the point angle can be taken,together with other values indicated herein, asdenitive of the presentinvention.

Attack angle As a result of my investigations I have determined that theattack angle, angle S, between the plane of the fluke forward faces anda plane passed through cable attachment point A of the shank and thecenters of area G-G offthe nuke forward faces, represents the effectiveangle of opposition of the fluke faces to the pull of the cable astransmitted through the pointpfcable attachment A.

In the lighter weight designs having a very low resistance to groundengagement and to which the anchor of this invention is particularlysuited, I have found that a considerable portion of the fluke area maybe located behind the pivot and the resistance to bun'al furtherreduced. In this instance, I have found the governing limitation isusually the point angle rather than the attack angle. For this reasonthe attack angle for this form should be kept in the range of 30-50.Because of the necessity of having a point angle of less than 75 it willge found that generally the attack angle will run below 45. Thismodifled form of anchor, wherein at least 35% of the area of the ukes isaft of the pivot axis about which the flukes are pivoted on the'shank,possesses the advantage that because the fluke area is approximatelybalanced fore and aft of the pivot axis. the vertical bending stressplaced on the shank is less permitting a lighter shank to be used withless burial resistance. approximately balanced fore and aft of thepivot, as employed herein and in the claims I mean that a materialportion of the moment of the fluke area forward of the pivot is balancedby the opposite moment of the fluke' area aft of the pivot. Obviously,the moment of the fluke area aft of the pivot cannot exceed the momentof the fluke area forward of the pivot; otherwise the tlukes rotate andtend/to assume an ineffective position parallel to the shank.

Fluke angle The value of this angie (angle T) is related to attack angleand shank length: i. e., the attack angle may be varied by changingeither the shank length or the fluke angle. If the fluke angle be toowide a desired attack angle is liable to require an excessively longshank, which has an advantage in'breaking out the anchor by By the term.

angle is too large for dependable initial engagement. While I considerthe uke angle of secondary importance, I prefer to keep it within thelimits 27 to 42.-

Relation of flake center spacing to shank length and to stock lengthspaced. I preferably keep this spacing to the minimum by the use of arelatively long and than 13%, and more preferably less than 10%,

reason of the greater leverage thus applied but-is narrow fluke and byplacing the inner edge of the fluke as close to the face of the shank aswill avoid undue danger of obstruction to the passage of the fluke pastthe shank. However, it is sometimes desirable to cause the flukes todiverge somewhat forwardly in order to overcome any tendency oftheanchor to furrow on its side in soft mud.

Shank length being taken as an approximate function of anchor size, thecenter s acing can be described as related to shank leng h. Il havefound by experiment that if this spacing (dimension P) exceeds 44% ofthe shank length (dimension K) the anchor will be unduly unstable andthrow an excessive corrective burden on the stock, which in turnincreases resistance area by necessitating a longer stock. I prefer tokeep ths'spacing below a third of the shank summation of importantcharacteristics By way of summaryand to further define the anchor ofthis invention, both with regard to its essential features and certainother features which, while not essential, are nevertheless important, Ihave indicated heretofore that the following are among thecharacteristics that should be observed A. The fluke area should not beless than 0.4 the resistance area. Preferably it should be not lessthanY 0.6 and even more preferably it should be greater than theresistance area and as much as 1.5 times vas much as the resistancearea.

B. lThe' resistance area should be less than 25% of, the square of theshank length, preferably less of the square of the shank length.

C. The point angle should be less than and preferably less than 70.

D. With the fluke area. approximately balanced about the pivot point,the attack angle should be in the range of 3050.

E. The stock vlength should be at least twice the distance between therespective centers of area ofthe nukes and preferably two and onehalf orthree times this distance.

Other characteristics Several other characteristics 'will now be con-Relation of stock length to shank length A minimum relation of stocklength to shank length is important to prevent skidding. If the 'stockbe too short the anchor may open on its side and rest on a three pointsupport consisting of one end of the shank, the end of the stock and thepoint or outer edge of the fluke. Length- Vening the stock tends to movethe center of gravity outside the base and to cause the anchor to fallflat, in which position initial engagement can take place. Themeasurement R (stock length) should not be less than about eight-tenthsof the shank length (measurement K) to prevent skidding with certaintyunder adverse conditions.

The flukes are preferably approximately triangular in shape because thisprovides a maximum area consistent with a uniformly low resistance toburial. The angle X between the inner and the outer forward edges of thefluke is preferably about 21 to 27, this being the range within whichsufficient fluke area can be provided without too greatly increasing theburial resistance. Also, the inner edge of each fluke diverges outwardlyat an angle of between and 15 because this has a beneficial effect inreducing skidding.

The fiukes are as thin as the material of which they are made willpermit. Preferably, they are substantially uniform in thicknesson anyline parallel to the shank axis, and are gently tapered in crosssection.

Fluke clearance The clearance between the fluke and the side of theshank cannot be too small without incurring serious risk of the flukesbeing held up in a position above the shank by an accumulation of stiifmud or sticky gravel on the shank, which would render theukesinoperative. I

prefer to keep the average clearance between the inner edge of the flukeand the side of the shank at more than two percent of the shank length,and in no case should it be less than one percent of the shank length.

Design of crown The structure of the crown is important. It ispreferable that the faces arranged to produce lift be sloped upwardlyopposite to the direction of dragging. If the angle of the faces is toosteep, they act as grips and prevent burial. They are preferably slopedat about 35 and between 25 and 45 is a good range. It is also desirablethat they be centrally located, i. e., on or close to the crown. If suchfaces be spaced any material distance from the crown, even if thedisposition is completely symmetrical, they are almost certain'to set upa tendency toward rotation under certain conditions. On the other hand,any portions of these faces lying directly under or back of the shankare liable to be rendered ineffective by the trenching effect of theforward end of the shank, lift being required solely in advance ofengagement and therefore at a time when there is no resistance to causethe forward end of the shank to lift away from the ground.kConsequently, the faces producing lift should be symmetrically locatedas regards the shank axis and as close thereto as is conof the shank.

Contour and location of stock To provide means for preventing the anchorfrom riding on its side, for positioning the fiukes to engage and enterthe ground and for stabiliz` ing the anchor when 'engaged and preventingrotation, I provide extensions laterally on each side of the shank. Inthe forms of anchors shown in Figures 1, 2 and 3 the lateral extensionsare provided as portions ofthe flukes. In either case, the terms "stockor stabilizing bar are applied herein and in the. claims-to such A stockof circular section or one in which the faces are arcuate in form ispreferred as combining strength with minimum resistance. However, anyform can be used which will not give undue resistance or introduce anunbalancing effect sufficient to cause rotation.k

It is also preferable to project the stabilizing bar from the after endof the anchor, as illustrated, though the more common practice ofprojecting it from the forward end of the shank may be followed ifdesired. In such location the advantage of being able to stow the anchorby drawing it into a hawse-pipe is lost. A stock forward also increasesthe resistance to burial of the forward end.

An anchor constructed in-accordance with the` above specification andwithin the limits defined by the appended claims will also bk founddesirable in the following respects, to wit: freedom from danger offouling the cable when the boat is ranging with wind or tide; ability tostow the anchor by hauling it into a hawse-pipe; ability to stow theanchor vflat on deck without the necessity for folding of nukes orstock; immediate readiness for use at all times; freedom from risk ofdamaging the hull when bringing the anchor on deck; great rapidity' andentire certainty of engagement in any type of holding ground; readydisengagement when it is desired to weigh the anchor, and a holdingpower per unit of weight far higher than any heretofore known. 'I'heanchor shown and described herein has been set forth correctly withrespect to the size, shape and relative relation of the various elementsthereof, particularly the showing of the drawing.

1. An anchor of the twin` fluke type comprise ing a shank having aforward and an after end with a point of cable attachment at saidforward end, a pair of ukes joined together to form a one piecestructure with each fluke fixed relative to the other, a pivot mountingsaid flukes on said shank at said after end with said ukes extend-r atan angle thereto of between 25 and 45 and terminating at a point raisedabove the fluke faces to slide along the ground and rotate the nukeswhen the anchor is on the ground with the flukes and shank insubstantially the same plane, saidshank and ukes being so proportioneoland positioned relative to each other when` I in operative position thatthe area of said flukes is approximately balanced about said pivot withat least 35% of the area of the fiukes aft of said pivot, and a plane,passed through said point of cable attachment and through the centers ofarea of the uke forward faces makes an angle with the plane of saidforward fluke faces in the range of substantially 30 to 50, said stockhaving an overall length at least twice the distance between therespective centers of area of the entire fluke forward faces, the area`of said entire fluke forward faces being at least 60% of the resistancearea of said anchor, as herein defined. f Y v I 2. An anchor of the twinfluke type comprising a shank having a forward and an after end with apoint of cable attachment at said forwardend, a pair of fiukes joinedtogether to form a one piece structure with each fluke fixed relative tothe other, a pivot mounting said ilukes on said shank at said after endwith said flukes extending toward said forward end and with said shankbetween said fiukes, and a stock adjacent the after end of said flukes,said flukes substantially simultaneously engaging the ground when inoperative position, each fluke having a major forward portionapproximately triangular in outline with the two forwardedgesapproaching each other at an angle approximately between 21 and 27, saidshank and fiukes being so proportioned and positioned relative to eachother when in operative position that the area of saidiiukes isapproximately balanced about said pivot with at least 35% of said area.aft of said pivot, and a plane, passed through said point of cableattachment and through the centers of area of the uke forward facesmakes an angle with the plane of said forward fluke faces in the rangeof substantially 30 to 50, said stock having an overall length at leasttwice the 1 distance between the respective centers of area of theentire uke forward faces, the area of said entire fluke forward facesbeing at least 60% of the resistance area of said anchor, as hereindefined.

3. An anchor of the twin iiuke type comprising a shank having a forwardand an after end with a point of cable attachment at said forward end, apair of flukes joined together to form a one piece structure with eachfluke xed relative to the other, a pivot mounting said flukes on saidshank at said after end with said flukes extending toward said forwardend and with said shank between said fiukes, and a stock adjacent theafter end of said flukes, said flukes substantially simultaneouslyengaging the ground when in operative position, said shank and ukesbeing so proportioned and positioned relative to each other when inoperative position that the area of said fiukes is .approximatelybalanced about said pivot with at least 35% thereof aft of said pivot,and a plane, passed through said point of cable attachment and throughthe forward ends of the flukes in operative position makes an angle withthe plane of said forward fluke faces of less than 75, said stock havingan overall length at least twice the distance between the respectivecenters of area of the entire fluke forward faces, the resistance areaof said anchor, as herein defined, being less than 25% of the square ofthe shank length.

4. An anchor of the twin fluke type comprising a shank having a forwardand an after end with a point of cable attachment at said forward end, apair of fiukes joined together to form a one piece structure with eachfiuke fixed relative to the other, a stock integral with said flukes andadjacent the' afterend thereof, and a pivot mounting said flukes on saidshank at said after end with said flukes extending toward said forwardend and with said shank between said iiukes, said iiukes substantiallysimultaneously engaging the ground when in operative position; saidshank and fiukes being so proportioned and positioned relative to eachother when in operative position that the area of said flukes isapproximately balanced about said pivot with at least 35% of said areaaft of said pivot, a plane, passed through said point of cableattachment and through the centers of area of the entire fluke forwardfaces makes an angle with the plane of said forward fluke faces in therange of substantially 30 to 50, and the total area of said flukeforward faces is at least 60% ofthe resistance area, as herein defined;said stock having an overall length at least twice the distance betweenthe respective centers of area of the entire forward faces of saidflukes.

5. An anchor of the twin iiuke type comprising a shank having a forwardand an after end with a point of cable attachment at said forward end, apair of fiukes joined together to form a one piece structure with eachfluke fixed relative to the other, a pivot mounting for said fiukes onsaid shank at said after end with said iiukes extending toward saidforward end and with said shank moving between said iiukes, said flukessubstantially simultaneously engaging the ground when in operativeposition, and a stock adjacent the after end of said fiukes; said shankand fiukes being so proportioned and positioned relative to each otherwhen in operative position that the area of said flukes is substantiallybalanced about said pivot mounting with at least 35% of the area of saidfukes aft of said pivot, and a plane, passed through said point of cableattachment and through the centers of area of the entire fluke forwardfaces makes an angle with the plane of said forward fluke faces in therange of substantially 30 to 50, and the total area of said flukeforward faces is at least 60% of the resistance area, as herein defined,said stock having an overall length at least two and a half times thedistance between the respective centers of area of the entire forwardfaces of said flukes.

6. An, anchor of the twin fluke type comprising a shank having a forwardand an after end with a point of cable attachment at said forward end, apair of ukes joined together to form a one piece structure with eachfluke fixed relative to the other, a pivot mounting said fiukes on saidshank at said after end with said fiukes extending toward said forwardend and with said shank between said flukes, and a stock adjacent theafter end of said fiukes, said flukes substantially simultaneouslyengaging the ground when in operative position; said shank and ilukesbeing so proportioned and positioned that the area of said ukes isapproximately balancedthat the area of balanced about said pivot 'and atleast 35% is 7. An anchor o! the twin nuke type comprising a shankhaving a forward and an after end with a point vof cable attachment atsaid forward end, a pair voi' nukes joined together to form a one piecestructure with each nuke nxed relative vto the other, a pivot mountingsaid nukes on said shank at said after end with said nukes lextendingtoward said forward end and with said shank between said nukes, and astock adjacent the after end of said nukes, said nukes substantiallysimultaneously engaging the ground when in operative position, saidshank and nukes being so proportioned and positioned relative to eachother when in operative position said nukes is approximately aft of saidpivot and a plane, passed through said point of cable attachment andthrough the centers of area of the entire nukeforward faces makes anangle with the plane of said forward nuke faces inthe range ofsubstantially 30 to 50, the area of said entire nuke forward faces beingat least equal to the resistance area of said anchor, as herein denned,and the distance between the entire nuke forward faces is less than 44%of the length oi' said shank.

8. An anchor of the Itwin nuke type, comprising a shank having a forwardand an after end with a point of cable attachment at said forward end, astock, a pair of nukes joined together to form a one piece structurewith each nuke nxed respective centers of area of the f end with arelative to the other, and a pivot mounting said nukes on said `shank atsaid afterend with said nukes extending toward said forward end and withsaid shank between said nukes, said` nukes substantially simultaneouslyengaging the ground when in operative position, said shank and nukeslbeing so proportioned and positioned relative to each other when inoperative position that the area of said nukes is substantially balancedabout said pivot with atleast oi' the area thereof aft of said pivot, a.plane, passed through said point of 'cable attachment and through thecenters of area of the entire nuke forward faces makes an angle with theplane of said forward nuke faces in the range of substantially 30 tosaid stock having an overall length at least two and a half times thedistance between the Vrespective centers of area of the entire forwardfaces of said nukes, the resistance area of said anchor, as hereindennedbeing less than 25% of the square of the shank length.

'an overall length v between the respective centers of area of-the 9. Ananchor of the twin nuke type oo prising a shank having a forward and anafter point of cable attachment at said forward end, a pair oi' nukesJoined together to form a one piece structure with each nuke fixedrelative to the other, a pivot mounting for said nukes on said shank atsaid aiter end with said nukes extending toward said forward end andwith said shank between said nukes, and a stock at the after end of saidnukes, said nukes substantially simultaneously engaging the ground whenin operative position; said, shank and nukes being so proportioned vandpositioned that the area of said nukes is approximately balanced aboutsaid pivot with at least 35% of saidv area aft of said pivot, the total`area of the entire nuke forward faces is at least equal tothe resistancearea, as herein denned, said stock having atleast twice the distanceentire forward faces of said. nukes, anda plane passed through saidcable attachment point and thefforward ends of said nukes in operativeposition makes an angle with the projected nukefforward faces of lessthan 10. An anchor of prising a shank `having a forward and an after endwith a point of cable attachment at said forward end, a stock, a pair ofnukes joined together to form a one piece structure` with veach nukenxed relative to the other, and a pivot mounting said nukes on saidshank at said after end with said nukes extending toward said forwardend and with said shank between said nukes, said nukes substantiallysimultaneously engaging the ground when in operative position, saidshank and nukes being so proportioned and positioned relative to eachother when in operative position that the area of said nukes issubstantially balanced about said pivot with at least 35% of the areathereof aft of said pivot, a plane, passed through saidpoint of cableattachment and through the centers of area of the entire nuke forwardfaces makes an angle with the plane of said forward nuke .faces in therange of substantially 30 to 50, said stock l having an overall lengthat least twice the distance between the respective centers oi area ofthe entire forward faces of said nukes, vthe area oi' said nukes beingat least 60% area of said anchor, as herein defined.

RICHARD S. DANFOR'I'H.

the twin nuke type, comof the resistance

